Blast furnace coke is essential in blast furnace operations, as a heat source for melting mineral ores, as a reducing agent for reducing iron ore to obtain iron, and as a high temperature resistant support material for maintaining gas permeability and melt permeability within the blast furnace. Accordingly, the coke requires sufficiently high strength to withstand the pressure of the packed bed inside the blast furnace while achieving a high degree of porosity, and must have a high level of abrasion resistance that satisfactorily minimizes the generation of fine powder. In order to produce this type of coke that exhibits superior strength and abrasion resistance and is capable of maintaining favorable porosity, not less than a certain proportion of a strongly caking coal is preferably included within the raw material coal used for coke production. However, there are limitations on the production of such strongly caking coal in terms of the production locality, quantity and cost, and it is anticipated that resource depletion may also become problematic in the near future. Consequently, it is desirable to reduce the amount of strongly caking coal within the raw material coal used for coke production.
Crude oil is generally subjected to atmospheric distillation during the refining process, thereby fractionating the crude oil into gas, LPG, naphtha, kerosene, light gas oil, heavy gas oil, and an atmospheric residue.
The naphtha, which is separated from the other components such as the atmospheric residue by performing an atmospheric distillation of the crude oil, is usually subjected to removal of the sulfur component within a hydrotreating unit, and subsequently separated into a light naphtha and a heavy naphtha. The heavy naphtha is reformed in a catalytic reformer unit, generating a reformate containing mainly aromatic hydrocarbons. Subsequently, the reformate is separated by a fractionator into a light reformate containing mainly hydrocarbons with a carbon number of 5 and a fraction containing mainly aromatic hydrocarbons with a carbon number of 6 or greater.
Further, the atmospheric residue that is separated from the other components by performing an atmospheric distillation of the crude oil is usually subjected to subsequent distillation under reduced pressure using a vacuum distillation unit. The vacuum residue that is separated from the other components by subjecting the atmospheric residue to a vacuum distillation is then further purified using a solvent extraction process known as an SDA (Solvent Deasphalting) process, a thermal decomposition process such as the Eureka Process or a coker process, or some other form of process.
In the SDA process of a vacuum residue, a solvent is used to selectively separate and remove the maltene fraction composed of the comparatively low molecular weight oils and resins that constitute the vacuum residue, while the asphaltenes having alkyl side chains and hydrogens contained within the vacuum residue are concentrated, thus producing a viscous SDA pitch.
Furthermore, when a thermal decomposition process is performed on the vacuum residue, thermal decomposition reactions of the vacuum residue cause a separation into a light oil having a high hydrogen content and a petroleum pitch having a high carbon content and high softening point such as Eureka pitch. When the vacuum residue is subjected to the thermal decomposition process, a dehydrogenation reaction occurs, and the side chains of the asphaltenes contained within the vacuum residue undergo dealkylation via a thermal decomposition reaction. Accordingly, the asphaltenes contained within the petroleum pitch are modified forms of the asphaltenes contained within the vacuum residue, and are typically highly aromatic compounds that have undergone polycondensation.
Conventionally, a caking additive for coke production formed from a petroleum pitch such as Eureka pitch is added to the raw material coal during the production of coke for iron production, and it is known that this addition enables the blend proportion of non-caking coal or slightly caking coal within the raw material coal to be increased. Further, coke production caking additives in which the modification of the asphaltenes is minimal and for which the co-carbonization reaction with coal readily generates optically anisotropic structures are preferred, and by using such caking additives, the strength of the coke can be increased, and the blend proportion of non-caking coal or slightly caking coal can be increased (see Non-Patent Document 1).
Examples of coke production caking additives that employ crude oil as the raw material include the caking additives disclosed in Patent Documents 1 to 4.
Patent Document 1 discloses a technique in which a deasphalted asphalt having a softening point of not less than 100° C., which is obtained from a petroleum-based heavy oil using butane, pentane or hexane, either alone or within a mixture, as a solvent, is added and blended as a caking additive.
Patent Document 2 discloses a process for producing an artificial caking coal in which a deasphalted asphalt extracted using butane, pentane or hexane as a solvent is reformed by heat treatment.
Further, Patent Document 3 discloses a caking filler containing more than 20% but not more than 90% of a hexane-soluble component and not more than 1% of a toluene-insoluble component, wherein the remainder is composed of a component that is insoluble in hexane and soluble in toluene, and an unavoidable residue component.
Furthermore, Patent Document 4 discloses a process for producing a caking additive for coke production, the process including a first step of separating a light oil from a petroleum-based heavy oil by solvent extraction or a distillation treatment to obtain a petroleum pitch, a second step of subjecting the petroleum pitch to a hydrogenation reforming treatment to obtain a reformed material, and a third step of separating the reformed material into a light oil and a heavy residue by solvent extraction or a distillation extraction.